/*-------------------------------------------------------------------------
 *
 * deparse.c
 *          Query deparser for postgres_fdw
 *
 * This file includes functions that examine query WHERE clauses to see
 * whether they're safe to send to the remote server for execution, as
 * well as functions to construct the query text to be sent.  The latter
 * functionality is annoyingly duplicative of ruleutils.c, but there are
 * enough special considerations that it seems best to keep this separate.
 * One saving grace is that we only need deparse logic for node types that
 * we consider safe to send.
 *
 * We assume that the remote session's search_path is exactly "pg_catalog",
 * and thus we need schema-qualify all and only names outside pg_catalog.
 *
 * We do not consider that it is ever safe to send COLLATE expressions to
 * the remote server: it might not have the same collation names we do.
 * (Later we might consider it safe to send COLLATE "C", but even that would
 * fail on old remote servers.)  An expression is considered safe to send
 * only if all operator/function input collations used in it are traceable to
 * Var(s) of the foreign table.  That implies that if the remote server gets
 * a different answer than we do, the foreign table's columns are not marked
 * with collations that match the remote table's columns, which we can
 * consider to be user error.
 *
 * Portions Copyright (c) 2012-2017, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *          contrib/postgres_fdw/deparse.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "postgres_fdw.h"

#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "commands/defrem.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/plannodes.h"
#include "optimizer/clauses.h"
#include "optimizer/prep.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/syscache.h"
#include "utils/typcache.h"


/*
 * Global context for foreign_expr_walker's search of an expression tree.
 */
typedef struct foreign_glob_cxt
{
    PlannerInfo *root;            /* global planner state */
    RelOptInfo *foreignrel;        /* the foreign relation we are planning for */
    Relids        relids;            /* relids of base relations in the underlying
                                 * scan */
} foreign_glob_cxt;

/*
 * Local (per-tree-level) context for foreign_expr_walker's search.
 * This is concerned with identifying collations used in the expression.
 */
typedef enum
{
    FDW_COLLATE_NONE,            /* expression is of a noncollatable type, or
                                 * it has default collation that is not
                                 * traceable to a foreign Var */
    FDW_COLLATE_SAFE,            /* collation derives from a foreign Var */
    FDW_COLLATE_UNSAFE            /* collation is non-default and derives from
                                 * something other than a foreign Var */
} FDWCollateState;

typedef struct foreign_loc_cxt
{
    Oid            collation;        /* OID of current collation, if any */
    FDWCollateState state;        /* state of current collation choice */
} foreign_loc_cxt;

/*
 * Context for deparseExpr
 */
typedef struct deparse_expr_cxt
{
    PlannerInfo *root;            /* global planner state */
    RelOptInfo *foreignrel;        /* the foreign relation we are planning for */
    RelOptInfo *scanrel;        /* the underlying scan relation. Same as
                                 * foreignrel, when that represents a join or
                                 * a base relation. */
    StringInfo    buf;            /* output buffer to append to */
    List      **params_list;    /* exprs that will become remote Params */
} deparse_expr_cxt;

#define REL_ALIAS_PREFIX    "r"
/* Handy macro to add relation name qualification */
#define ADD_REL_QUALIFIER(buf, varno)    \
        appendStringInfo((buf), "%s%d.", REL_ALIAS_PREFIX, (varno))
#define SUBQUERY_REL_ALIAS_PREFIX    "s"
#define SUBQUERY_COL_ALIAS_PREFIX    "c"

/*
 * Functions to determine whether an expression can be evaluated safely on
 * remote server.
 */
static bool foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt);
static char *deparse_type_name(Oid type_oid, int32 typemod);

/*
 * Functions to construct string representation of a node tree.
 */
static void deparseTargetList(StringInfo buf,
                  PlannerInfo *root,
                  Index rtindex,
                  Relation rel,
                  bool is_returning,
                  Bitmapset *attrs_used,
                  bool qualify_col,
                  List **retrieved_attrs);
static void deparseExplicitTargetList(List *tlist, List **retrieved_attrs,
                          deparse_expr_cxt *context);
static void deparseSubqueryTargetList(deparse_expr_cxt *context);
static void deparseReturningList(StringInfo buf, PlannerInfo *root,
                     Index rtindex, Relation rel,
                     bool trig_after_row,
                     List *returningList,
                     List **retrieved_attrs);
static void deparseColumnRef(StringInfo buf, int varno, int varattno,
                 PlannerInfo *root, bool qualify_col);
static void deparseRelation(StringInfo buf, Relation rel);
static void deparseExpr(Expr *expr, deparse_expr_cxt *context);
static void deparseVar(Var *node, deparse_expr_cxt *context);
static void deparseConst(Const *node, deparse_expr_cxt *context, int showtype);
static void deparseParam(Param *node, deparse_expr_cxt *context);
static void deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context);
static void deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context);
static void deparseOpExpr(OpExpr *node, deparse_expr_cxt *context);
static void deparseOperatorName(StringInfo buf, Form_pg_operator opform);
static void deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context);
static void deparseScalarArrayOpExpr(ScalarArrayOpExpr *node,
                         deparse_expr_cxt *context);
static void deparseRelabelType(RelabelType *node, deparse_expr_cxt *context);
static void deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context);
static void deparseNullTest(NullTest *node, deparse_expr_cxt *context);
static void deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context);
static void printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                 deparse_expr_cxt *context);
static void printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                       deparse_expr_cxt *context);
static void deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
                 deparse_expr_cxt *context);
static void deparseLockingClause(deparse_expr_cxt *context);
static void appendOrderByClause(List *pathkeys, deparse_expr_cxt *context);
static void appendConditions(List *exprs, deparse_expr_cxt *context);
static void deparseFromExprForRel(StringInfo buf, PlannerInfo *root,
                      RelOptInfo *joinrel, bool use_alias, List **params_list);
static void deparseFromExpr(List *quals, deparse_expr_cxt *context);
static void deparseRangeTblRef(StringInfo buf, PlannerInfo *root,
                   RelOptInfo *foreignrel, bool make_subquery,
                   List **params_list);
static void deparseAggref(Aggref *node, deparse_expr_cxt *context);
static void appendGroupByClause(List *tlist, deparse_expr_cxt *context);
static void appendAggOrderBy(List *orderList, List *targetList,
                 deparse_expr_cxt *context);
static void appendFunctionName(Oid funcid, deparse_expr_cxt *context);
static Node *deparseSortGroupClause(Index ref, List *tlist,
                       deparse_expr_cxt *context);

/*
 * Helper functions
 */
static bool is_subquery_var(Var *node, RelOptInfo *foreignrel,
                int *relno, int *colno);
static void get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                              int *relno, int *colno);


/*
 * Examine each qual clause in input_conds, and classify them into two groups,
 * which are returned as two lists:
 *    - remote_conds contains expressions that can be evaluated remotely
 *    - local_conds contains expressions that can't be evaluated remotely
 */
void
classifyConditions(PlannerInfo *root,
                   RelOptInfo *baserel,
                   List *input_conds,
                   List **remote_conds,
                   List **local_conds)
{
    ListCell   *lc;

    *remote_conds = NIL;
    *local_conds = NIL;

    foreach(lc, input_conds)
    {
        RestrictInfo *ri = lfirst_node(RestrictInfo, lc);

        if (is_foreign_expr(root, baserel, ri->clause))
            *remote_conds = lappend(*remote_conds, ri);
        else
            *local_conds = lappend(*local_conds, ri);
    }
}

/*
 * Returns true if given expr is safe to evaluate on the foreign server.
 */
bool
is_foreign_expr(PlannerInfo *root,
                RelOptInfo *baserel,
                Expr *expr)
{
    foreign_glob_cxt glob_cxt;
    foreign_loc_cxt loc_cxt;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) (baserel->fdw_private);

    /*
     * Check that the expression consists of nodes that are safe to execute
     * remotely.
     */
    glob_cxt.root = root;
    glob_cxt.foreignrel = baserel;

    /*
     * For an upper relation, use relids from its underneath scan relation,
     * because the upperrel's own relids currently aren't set to anything
     * meaningful by the core code.  For other relation, use their own relids.
     */
    if (IS_UPPER_REL(baserel))
        glob_cxt.relids = fpinfo->outerrel->relids;
    else
        glob_cxt.relids = baserel->relids;
    loc_cxt.collation = InvalidOid;
    loc_cxt.state = FDW_COLLATE_NONE;
    if (!foreign_expr_walker((Node *) expr, &glob_cxt, &loc_cxt))
        return false;

    /*
     * If the expression has a valid collation that does not arise from a
     * foreign var, the expression can not be sent over.
     */
    if (loc_cxt.state == FDW_COLLATE_UNSAFE)
        return false;

    /*
     * An expression which includes any mutable functions can't be sent over
     * because its result is not stable.  For example, sending now() remote
     * side could cause confusion from clock offsets.  Future versions might
     * be able to make this choice with more granularity.  (We check this last
     * because it requires a lot of expensive catalog lookups.)
     */
    if (contain_mutable_functions((Node *) expr))
        return false;

    /* OK to evaluate on the remote server */
    return true;
}

/*
 * Check if expression is safe to execute remotely, and return true if so.
 *
 * In addition, *outer_cxt is updated with collation information.
 *
 * We must check that the expression contains only node types we can deparse,
 * that all types/functions/operators are safe to send (they are "shippable"),
 * and that all collations used in the expression derive from Vars of the
 * foreign table.  Because of the latter, the logic is pretty close to
 * assign_collations_walker() in parse_collate.c, though we can assume here
 * that the given expression is valid.  Note function mutability is not
 * currently considered here.
 */
static bool
foreign_expr_walker(Node *node,
                    foreign_glob_cxt *glob_cxt,
                    foreign_loc_cxt *outer_cxt)
{
    bool        check_type = true;
    PgFdwRelationInfo *fpinfo;
    foreign_loc_cxt inner_cxt;
    Oid            collation;
    FDWCollateState state;

    /* Need do nothing for empty subexpressions */
    if (node == NULL)
        return true;

    /* May need server info from baserel's fdw_private struct */
    fpinfo = (PgFdwRelationInfo *) (glob_cxt->foreignrel->fdw_private);

    /* Set up inner_cxt for possible recursion to child nodes */
    inner_cxt.collation = InvalidOid;
    inner_cxt.state = FDW_COLLATE_NONE;

    switch (nodeTag(node))
    {
        case T_Var:
            {
                Var           *var = (Var *) node;

                /*
                 * If the Var is from the foreign table, we consider its
                 * collation (if any) safe to use.  If it is from another
                 * table, we treat its collation the same way as we would a
                 * Param's collation, ie it's not safe for it to have a
                 * non-default collation.
                 */
                if (bms_is_member(var->varno, glob_cxt->relids) &&
                    var->varlevelsup == 0)
                {
                    /* Var belongs to foreign table */

                    /*
                     * System columns other than ctid and oid should not be
                     * sent to the remote, since we don't make any effort to
                     * ensure that local and remote values match (tableoid, in
                     * particular, almost certainly doesn't match).
                     */
                    if (var->varattno < 0 &&
                        var->varattno != SelfItemPointerAttributeNumber &&
                        var->varattno != ObjectIdAttributeNumber)
                        return false;

                    /* Else check the collation */
                    collation = var->varcollid;
                    state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
                }
                else
                {
                    /* Var belongs to some other table */
                    collation = var->varcollid;
                    if (collation == InvalidOid ||
                        collation == DEFAULT_COLLATION_OID)
                    {
                        /*
                         * It's noncollatable, or it's safe to combine with a
                         * collatable foreign Var, so set state to NONE.
                         */
                        state = FDW_COLLATE_NONE;
                    }
                    else
                    {
                        /*
                         * Do not fail right away, since the Var might appear
                         * in a collation-insensitive context.
                         */
                        state = FDW_COLLATE_UNSAFE;
                    }
                }
            }
            break;
        case T_Const:
            {
                Const       *c = (Const *) node;

                /*
                 * If the constant has nondefault collation, either it's of a
                 * non-builtin type, or it reflects folding of a CollateExpr.
                 * It's unsafe to send to the remote unless it's used in a
                 * non-collation-sensitive context.
                 */
                collation = c->constcollid;
                if (collation == InvalidOid ||
                    collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_Param:
            {
                Param       *p = (Param *) node;

                /*
                 * Collation rule is same as for Consts and non-foreign Vars.
                 */
                collation = p->paramcollid;
                if (collation == InvalidOid ||
                    collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_ArrayRef:
            {
                ArrayRef   *ar = (ArrayRef *) node;

                /* Assignment should not be in restrictions. */
                if (ar->refassgnexpr != NULL)
                    return false;

                /*
                 * Recurse to remaining subexpressions.  Since the array
                 * subscripts must yield (noncollatable) integers, they won't
                 * affect the inner_cxt state.
                 */
                if (!foreign_expr_walker((Node *) ar->refupperindexpr,
                                         glob_cxt, &inner_cxt))
                    return false;
                if (!foreign_expr_walker((Node *) ar->reflowerindexpr,
                                         glob_cxt, &inner_cxt))
                    return false;
                if (!foreign_expr_walker((Node *) ar->refexpr,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * Array subscripting should yield same collation as input,
                 * but for safety use same logic as for function nodes.
                 */
                collation = ar->refcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_FuncExpr:
            {
                FuncExpr   *fe = (FuncExpr *) node;

                /*
                 * If function used by the expression is not shippable, it
                 * can't be sent to remote because it might have incompatible
                 * semantics on remote side.
                 */
                if (!is_shippable(fe->funcid, ProcedureRelationId, fpinfo))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) fe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If function's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (fe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         fe->inputcollid != inner_cxt.collation)
                    return false;

                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)
                 */
                collation = fe->funccollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_OpExpr:
        case T_DistinctExpr:    /* struct-equivalent to OpExpr */
            {
                OpExpr       *oe = (OpExpr *) node;

                /*
                 * Similarly, only shippable operators can be sent to remote.
                 * (If the operator is shippable, we assume its underlying
                 * function is too.)
                 */
                if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;

                /* Result-collation handling is same as for functions */
                collation = oe->opcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_ScalarArrayOpExpr:
            {
                ScalarArrayOpExpr *oe = (ScalarArrayOpExpr *) node;

                /*
                 * Again, only shippable operators can be sent to remote.
                 */
                if (!is_shippable(oe->opno, OperatorRelationId, fpinfo))
                    return false;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) oe->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If operator's input collation is not derived from a foreign
                 * Var, it can't be sent to remote.
                 */
                if (oe->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         oe->inputcollid != inner_cxt.collation)
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_RelabelType:
            {
                RelabelType *r = (RelabelType *) node;

                /*
                 * Recurse to input subexpression.
                 */
                if (!foreign_expr_walker((Node *) r->arg,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * RelabelType must not introduce a collation not derived from
                 * an input foreign Var (same logic as for a real function).
                 */
                collation = r->resultcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_BoolExpr:
            {
                BoolExpr   *b = (BoolExpr *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) b->args,
                                         glob_cxt, &inner_cxt))
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_NullTest:
            {
                NullTest   *nt = (NullTest *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) nt->arg,
                                         glob_cxt, &inner_cxt))
                    return false;

                /* Output is always boolean and so noncollatable. */
                collation = InvalidOid;
                state = FDW_COLLATE_NONE;
            }
            break;
        case T_ArrayExpr:
            {
                ArrayExpr  *a = (ArrayExpr *) node;

                /*
                 * Recurse to input subexpressions.
                 */
                if (!foreign_expr_walker((Node *) a->elements,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * ArrayExpr must not introduce a collation not derived from
                 * an input foreign Var (same logic as for a function).
                 */
                collation = a->array_collid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        case T_List:
            {
                List       *l = (List *) node;
                ListCell   *lc;

                /*
                 * Recurse to component subexpressions.
                 */
                foreach(lc, l)
                {
                    if (!foreign_expr_walker((Node *) lfirst(lc),
                                             glob_cxt, &inner_cxt))
                        return false;
                }

                /*
                 * When processing a list, collation state just bubbles up
                 * from the list elements.
                 */
                collation = inner_cxt.collation;
                state = inner_cxt.state;

                /* Don't apply exprType() to the list. */
                check_type = false;
            }
            break;
        case T_Aggref:
            {
                Aggref       *agg = (Aggref *) node;
                ListCell   *lc;

                /* Not safe to pushdown when not in grouping context */
                if (!IS_UPPER_REL(glob_cxt->foreignrel))
                    return false;

                /* Only non-split aggregates are pushable. */
                if (agg->aggsplit != AGGSPLIT_SIMPLE)
                    return false;

                /* As usual, it must be shippable. */
                if (!is_shippable(agg->aggfnoid, ProcedureRelationId, fpinfo))
                    return false;

                /*
                 * Recurse to input args. aggdirectargs, aggorder and
                 * aggdistinct are all present in args, so no need to check
                 * their shippability explicitly.
                 */
                foreach(lc, agg->args)
                {
                    Node       *n = (Node *) lfirst(lc);

                    /* If TargetEntry, extract the expression from it */
                    if (IsA(n, TargetEntry))
                    {
                        TargetEntry *tle = (TargetEntry *) n;

                        n = (Node *) tle->expr;
                    }

                    if (!foreign_expr_walker(n, glob_cxt, &inner_cxt))
                        return false;
                }

                /*
                 * For aggorder elements, check whether the sort operator, if
                 * specified, is shippable or not.
                 */
                if (agg->aggorder)
                {
                    ListCell   *lc;

                    foreach(lc, agg->aggorder)
                    {
                        SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
                        Oid            sortcoltype;
                        TypeCacheEntry *typentry;
                        TargetEntry *tle;

                        tle = get_sortgroupref_tle(srt->tleSortGroupRef,
                                                   agg->args);
                        sortcoltype = exprType((Node *) tle->expr);
                        typentry = lookup_type_cache(sortcoltype,
                                                     TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
                        /* Check shippability of non-default sort operator. */
                        if (srt->sortop != typentry->lt_opr &&
                            srt->sortop != typentry->gt_opr &&
                            !is_shippable(srt->sortop, OperatorRelationId,
                                          fpinfo))
                            return false;
                    }
                }

                /* Check aggregate filter */
                if (!foreign_expr_walker((Node *) agg->aggfilter,
                                         glob_cxt, &inner_cxt))
                    return false;

                /*
                 * If aggregate's input collation is not derived from a
                 * foreign Var, it can't be sent to remote.
                 */
                if (agg->inputcollid == InvalidOid)
                     /* OK, inputs are all noncollatable */ ;
                else if (inner_cxt.state != FDW_COLLATE_SAFE ||
                         agg->inputcollid != inner_cxt.collation)
                    return false;

                /*
                 * Detect whether node is introducing a collation not derived
                 * from a foreign Var.  (If so, we just mark it unsafe for now
                 * rather than immediately returning false, since the parent
                 * node might not care.)
                 */
                collation = agg->aggcollid;
                if (collation == InvalidOid)
                    state = FDW_COLLATE_NONE;
                else if (inner_cxt.state == FDW_COLLATE_SAFE &&
                         collation == inner_cxt.collation)
                    state = FDW_COLLATE_SAFE;
                else if (collation == DEFAULT_COLLATION_OID)
                    state = FDW_COLLATE_NONE;
                else
                    state = FDW_COLLATE_UNSAFE;
            }
            break;
        default:

            /*
             * If it's anything else, assume it's unsafe.  This list can be
             * expanded later, but don't forget to add deparse support below.
             */
            return false;
    }

    /*
     * If result type of given expression is not shippable, it can't be sent
     * to remote because it might have incompatible semantics on remote side.
     */
    if (check_type && !is_shippable(exprType(node), TypeRelationId, fpinfo))
        return false;

    /*
     * Now, merge my collation information into my parent's state.
     */
    if (state > outer_cxt->state)
    {
        /* Override previous parent state */
        outer_cxt->collation = collation;
        outer_cxt->state = state;
    }
    else if (state == outer_cxt->state)
    {
        /* Merge, or detect error if there's a collation conflict */
        switch (state)
        {
            case FDW_COLLATE_NONE:
                /* Nothing + nothing is still nothing */
                break;
            case FDW_COLLATE_SAFE:
                if (collation != outer_cxt->collation)
                {
                    /*
                     * Non-default collation always beats default.
                     */
                    if (outer_cxt->collation == DEFAULT_COLLATION_OID)
                    {
                        /* Override previous parent state */
                        outer_cxt->collation = collation;
                    }
                    else if (collation != DEFAULT_COLLATION_OID)
                    {
                        /*
                         * Conflict; show state as indeterminate.  We don't
                         * want to "return false" right away, since parent
                         * node might not care about collation.
                         */
                        outer_cxt->state = FDW_COLLATE_UNSAFE;
                    }
                }
                break;
            case FDW_COLLATE_UNSAFE:
                /* We're still conflicted ... */
                break;
        }
    }

    /* It looks OK */
    return true;
}

/*
 * Convert type OID + typmod info into a type name we can ship to the remote
 * server.  Someplace else had better have verified that this type name is
 * expected to be known on the remote end.
 *
 * This is almost just format_type_with_typemod(), except that if left to its
 * own devices, that function will make schema-qualification decisions based
 * on the local search_path, which is wrong.  We must schema-qualify all
 * type names that are not in pg_catalog.  We assume here that built-in types
 * are all in pg_catalog and need not be qualified; otherwise, qualify.
 */
static char *
deparse_type_name(Oid type_oid, int32 typemod)
{
    if (is_builtin(type_oid))
        return format_type_with_typemod(type_oid, typemod);
    else
        return format_type_with_typemod_qualified(type_oid, typemod);
}

/*
 * Build the targetlist for given relation to be deparsed as SELECT clause.
 *
 * The output targetlist contains the columns that need to be fetched from the
 * foreign server for the given relation.  If foreignrel is an upper relation,
 * then the output targetlist can also contain expressions to be evaluated on
 * foreign server.
 */
List *
build_tlist_to_deparse(RelOptInfo *foreignrel)
{
    List       *tlist = NIL;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    ListCell   *lc;

    /*
     * For an upper relation, we have already built the target list while
     * checking shippability, so just return that.
     */
    if (IS_UPPER_REL(foreignrel))
        return fpinfo->grouped_tlist;

    /*
     * We require columns specified in foreignrel->reltarget->exprs and those
     * required for evaluating the local conditions.
     */
    tlist = add_to_flat_tlist(tlist,
                              pull_var_clause((Node *) foreignrel->reltarget->exprs,
                                              PVC_RECURSE_PLACEHOLDERS));
    foreach(lc, fpinfo->local_conds)
    {
        RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);

        tlist = add_to_flat_tlist(tlist,
                                  pull_var_clause((Node *) rinfo->clause,
                                                  PVC_RECURSE_PLACEHOLDERS));
    }

    return tlist;
}

/*
 * Deparse SELECT statement for given relation into buf.
 *
 * tlist contains the list of desired columns to be fetched from foreign server.
 * For a base relation fpinfo->attrs_used is used to construct SELECT clause,
 * hence the tlist is ignored for a base relation.
 *
 * remote_conds is the list of conditions to be deparsed into the WHERE clause
 * (or, in the case of upper relations, into the HAVING clause).
 *
 * If params_list is not NULL, it receives a list of Params and other-relation
 * Vars used in the clauses; these values must be transmitted to the remote
 * server as parameter values.
 *
 * If params_list is NULL, we're generating the query for EXPLAIN purposes,
 * so Params and other-relation Vars should be replaced by dummy values.
 *
 * pathkeys is the list of pathkeys to order the result by.
 *
 * is_subquery is the flag to indicate whether to deparse the specified
 * relation as a subquery.
 *
 * List of columns selected is returned in retrieved_attrs.
 */
extern void
deparseSelectStmtForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *rel,
                        List *tlist, List *remote_conds, List *pathkeys,
                        bool is_subquery, List **retrieved_attrs,
                        List **params_list)
{
    deparse_expr_cxt context;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
    List       *quals;

    /*
     * We handle relations for foreign tables, joins between those and upper
     * relations.
     */
    Assert(IS_JOIN_REL(rel) || IS_SIMPLE_REL(rel) || IS_UPPER_REL(rel));

    /* Fill portions of context common to upper, join and base relation */
    context.buf = buf;
    context.root = root;
    context.foreignrel = rel;
    context.scanrel = IS_UPPER_REL(rel) ? fpinfo->outerrel : rel;
    context.params_list = params_list;

    /* Construct SELECT clause */
    deparseSelectSql(tlist, is_subquery, retrieved_attrs, &context);

    /*
     * For upper relations, the WHERE clause is built from the remote
     * conditions of the underlying scan relation; otherwise, we can use the
     * supplied list of remote conditions directly.
     */
    if (IS_UPPER_REL(rel))
    {
        PgFdwRelationInfo *ofpinfo;

        ofpinfo = (PgFdwRelationInfo *) fpinfo->outerrel->fdw_private;
        quals = ofpinfo->remote_conds;
    }
    else
        quals = remote_conds;

    /* Construct FROM and WHERE clauses */
    deparseFromExpr(quals, &context);

    if (IS_UPPER_REL(rel))
    {
        /* Append GROUP BY clause */
        appendGroupByClause(tlist, &context);

        /* Append HAVING clause */
        if (remote_conds)
        {
            appendStringInfo(buf, " HAVING ");
            appendConditions(remote_conds, &context);
        }
    }

    /* Add ORDER BY clause if we found any useful pathkeys */
    if (pathkeys)
        appendOrderByClause(pathkeys, &context);

    /* Add any necessary FOR UPDATE/SHARE. */
    deparseLockingClause(&context);
}

/*
 * Construct a simple SELECT statement that retrieves desired columns
 * of the specified foreign table, and append it to "buf".  The output
 * contains just "SELECT ... ".
 *
 * We also create an integer List of the columns being retrieved, which is
 * returned to *retrieved_attrs, unless we deparse the specified relation
 * as a subquery.
 *
 * tlist is the list of desired columns.  is_subquery is the flag to
 * indicate whether to deparse the specified relation as a subquery.
 * Read prologue of deparseSelectStmtForRel() for details.
 */
static void
deparseSelectSql(List *tlist, bool is_subquery, List **retrieved_attrs,
                 deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    RelOptInfo *foreignrel = context->foreignrel;
    PlannerInfo *root = context->root;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

    /*
     * Construct SELECT list
     */
    appendStringInfoString(buf, "SELECT ");

    if (is_subquery)
    {
        /*
         * For a relation that is deparsed as a subquery, emit expressions
         * specified in the relation's reltarget.  Note that since this is for
         * the subquery, no need to care about *retrieved_attrs.
         */
        deparseSubqueryTargetList(context);
    }
    else if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
    {
        /*
         * For a join or upper relation the input tlist gives the list of
         * columns required to be fetched from the foreign server.
         */
        deparseExplicitTargetList(tlist, retrieved_attrs, context);
    }
    else
    {
        /*
         * For a base relation fpinfo->attrs_used gives the list of columns
         * required to be fetched from the foreign server.
         */
        RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

        /*
         * Core code already has some lock on each rel being planned, so we
         * can use NoLock here.
         */
        Relation    rel = heap_open(rte->relid, NoLock);

        deparseTargetList(buf, root, foreignrel->relid, rel, false,
                          fpinfo->attrs_used, false, retrieved_attrs);
        heap_close(rel, NoLock);
    }
}

/*
 * Construct a FROM clause and, if needed, a WHERE clause, and append those to
 * "buf".
 *
 * quals is the list of clauses to be included in the WHERE clause.
 * (These may or may not include RestrictInfo decoration.)
 */
static void
deparseFromExpr(List *quals, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    RelOptInfo *scanrel = context->scanrel;

    /* For upper relations, scanrel must be either a joinrel or a baserel */
    Assert(!IS_UPPER_REL(context->foreignrel) ||
           IS_JOIN_REL(scanrel) || IS_SIMPLE_REL(scanrel));

    /* Construct FROM clause */
    appendStringInfoString(buf, " FROM ");
    deparseFromExprForRel(buf, context->root, scanrel,
                          (bms_num_members(scanrel->relids) > 1),
                          context->params_list);

    /* Construct WHERE clause */
    if (quals != NIL)
    {
        appendStringInfo(buf, " WHERE ");
        appendConditions(quals, context);
    }
}

/*
 * Emit a target list that retrieves the columns specified in attrs_used.
 * This is used for both SELECT and RETURNING targetlists; the is_returning
 * parameter is true only for a RETURNING targetlist.
 *
 * The tlist text is appended to buf, and we also create an integer List
 * of the columns being retrieved, which is returned to *retrieved_attrs.
 *
 * If qualify_col is true, add relation alias before the column name.
 */
static void
deparseTargetList(StringInfo buf,
                  PlannerInfo *root,
                  Index rtindex,
                  Relation rel,
                  bool is_returning,
                  Bitmapset *attrs_used,
                  bool qualify_col,
                  List **retrieved_attrs)
{
    TupleDesc    tupdesc = RelationGetDescr(rel);
    bool        have_wholerow;
    bool        first;
    int            i;

    *retrieved_attrs = NIL;

    /* If there's a whole-row reference, we'll need all the columns. */
    have_wholerow = bms_is_member(0 - FirstLowInvalidHeapAttributeNumber,
                                  attrs_used);

    first = true;
    for (i = 1; i <= tupdesc->natts; i++)
    {
        Form_pg_attribute attr = tupdesc->attrs[i - 1];

        /* Ignore dropped attributes. */
        if (attr->attisdropped)
            continue;

        if (have_wholerow ||
            bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            else if (is_returning)
                appendStringInfoString(buf, " RETURNING ");
            first = false;

            deparseColumnRef(buf, rtindex, i, root, qualify_col);

            *retrieved_attrs = lappend_int(*retrieved_attrs, i);
        }
    }

    /*
     * Add ctid and oid if needed.  We currently don't support retrieving any
     * other system columns.
     */
    if (bms_is_member(SelfItemPointerAttributeNumber - FirstLowInvalidHeapAttributeNumber,
                      attrs_used))
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        else if (is_returning)
            appendStringInfoString(buf, " RETURNING ");
        first = false;

        if (qualify_col)
            ADD_REL_QUALIFIER(buf, rtindex);
        appendStringInfoString(buf, "ctid");

        *retrieved_attrs = lappend_int(*retrieved_attrs,
                                       SelfItemPointerAttributeNumber);
    }
    if (bms_is_member(ObjectIdAttributeNumber - FirstLowInvalidHeapAttributeNumber,
                      attrs_used))
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        else if (is_returning)
            appendStringInfoString(buf, " RETURNING ");
        first = false;

        if (qualify_col)
            ADD_REL_QUALIFIER(buf, rtindex);
        appendStringInfoString(buf, "oid");

        *retrieved_attrs = lappend_int(*retrieved_attrs,
                                       ObjectIdAttributeNumber);
    }

    /* Don't generate bad syntax if no undropped columns */
    if (first && !is_returning)
        appendStringInfoString(buf, "NULL");
}

/*
 * Deparse the appropriate locking clause (FOR UPDATE or FOR SHARE) for a
 * given relation (context->scanrel).
 */
static void
deparseLockingClause(deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    PlannerInfo *root = context->root;
    RelOptInfo *rel = context->scanrel;
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) rel->fdw_private;
    int            relid = -1;

    while ((relid = bms_next_member(rel->relids, relid)) >= 0)
    {
        /*
         * Ignore relation if it appears in a lower subquery.  Locking clause
         * for such a relation is included in the subquery if necessary.
         */
        if (bms_is_member(relid, fpinfo->lower_subquery_rels))
            continue;

        /*
         * Add FOR UPDATE/SHARE if appropriate.  We apply locking during the
         * initial row fetch, rather than later on as is done for local
         * tables. The extra roundtrips involved in trying to duplicate the
         * local semantics exactly don't seem worthwhile (see also comments
         * for RowMarkType).
         *
         * Note: because we actually run the query as a cursor, this assumes
         * that DECLARE CURSOR ... FOR UPDATE is supported, which it isn't
         * before 8.3.
         */
        if (relid == root->parse->resultRelation &&
            (root->parse->commandType == CMD_UPDATE ||
             root->parse->commandType == CMD_DELETE))
        {
            /* Relation is UPDATE/DELETE target, so use FOR UPDATE */
            appendStringInfoString(buf, " FOR UPDATE");

            /* Add the relation alias if we are here for a join relation */
            if (IS_JOIN_REL(rel))
                appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
        }
        else
        {
            PlanRowMark *rc = get_plan_rowmark(root->rowMarks, relid);

            if (rc)
            {
                /*
                 * Relation is specified as a FOR UPDATE/SHARE target, so
                 * handle that.  (But we could also see LCS_NONE, meaning this
                 * isn't a target relation after all.)
                 *
                 * For now, just ignore any [NO] KEY specification, since (a)
                 * it's not clear what that means for a remote table that we
                 * don't have complete information about, and (b) it wouldn't
                 * work anyway on older remote servers.  Likewise, we don't
                 * worry about NOWAIT.
                 */
                switch (rc->strength)
                {
                    case LCS_NONE:
                        /* No locking needed */
                        break;
                    case LCS_FORKEYSHARE:
                    case LCS_FORSHARE:
                        appendStringInfoString(buf, " FOR SHARE");
                        break;
                    case LCS_FORNOKEYUPDATE:
                    case LCS_FORUPDATE:
                        appendStringInfoString(buf, " FOR UPDATE");
                        break;
                }

                /* Add the relation alias if we are here for a join relation */
                if (bms_num_members(rel->relids) > 1 &&
                    rc->strength != LCS_NONE)
                    appendStringInfo(buf, " OF %s%d", REL_ALIAS_PREFIX, relid);
            }
        }
    }
}

/*
 * Deparse conditions from the provided list and append them to buf.
 *
 * The conditions in the list are assumed to be ANDed. This function is used to
 * deparse WHERE clauses, JOIN .. ON clauses and HAVING clauses.
 *
 * Depending on the caller, the list elements might be either RestrictInfos
 * or bare clauses.
 */
static void
appendConditions(List *exprs, deparse_expr_cxt *context)
{
    int            nestlevel;
    ListCell   *lc;
    bool        is_first = true;
    StringInfo    buf = context->buf;

    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();

    foreach(lc, exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);

        /* Extract clause from RestrictInfo, if required */
        if (IsA(expr, RestrictInfo))
            expr = ((RestrictInfo *) expr)->clause;

        /* Connect expressions with "AND" and parenthesize each condition. */
        if (!is_first)
            appendStringInfoString(buf, " AND ");

        appendStringInfoChar(buf, '(');
        deparseExpr(expr, context);
        appendStringInfoChar(buf, ')');

        is_first = false;
    }

    reset_transmission_modes(nestlevel);
}

/* Output join name for given join type */
extern const char *
get_jointype_name(JoinType jointype)
{
    switch (jointype)
    {
        case JOIN_INNER:
            return "INNER";

        case JOIN_LEFT:
            return "LEFT";

        case JOIN_RIGHT:
            return "RIGHT";

        case JOIN_FULL:
            return "FULL";

        default:
            /* Shouldn't come here, but protect from buggy code. */
            elog(ERROR, "unsupported join type %d", jointype);
    }

    /* Keep compiler happy */
    return NULL;
}

/*
 * Deparse given targetlist and append it to context->buf.
 *
 * tlist is list of TargetEntry's which in turn contain Var nodes.
 *
 * retrieved_attrs is the list of continuously increasing integers starting
 * from 1. It has same number of entries as tlist.
 */
static void
deparseExplicitTargetList(List *tlist, List **retrieved_attrs,
                          deparse_expr_cxt *context)
{
    ListCell   *lc;
    StringInfo    buf = context->buf;
    int            i = 0;

    *retrieved_attrs = NIL;

    foreach(lc, tlist)
    {
        TargetEntry *tle = lfirst_node(TargetEntry, lc);

        if (i > 0)
            appendStringInfoString(buf, ", ");
        deparseExpr((Expr *) tle->expr, context);

        *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
        i++;
    }

    if (i == 0)
        appendStringInfoString(buf, "NULL");
}

/*
 * Emit expressions specified in the given relation's reltarget.
 *
 * This is used for deparsing the given relation as a subquery.
 */
static void
deparseSubqueryTargetList(deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    RelOptInfo *foreignrel = context->foreignrel;
    bool        first;
    ListCell   *lc;

    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

    first = true;
    foreach(lc, foreignrel->reltarget->exprs)
    {
        Node       *node = (Node *) lfirst(lc);

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        deparseExpr((Expr *) node, context);
    }

    /* Don't generate bad syntax if no expressions */
    if (first)
        appendStringInfoString(buf, "NULL");
}

/*
 * Construct FROM clause for given relation
 *
 * The function constructs ... JOIN ... ON ... for join relation. For a base
 * relation it just returns schema-qualified tablename, with the appropriate
 * alias if so requested.
 */
static void
deparseFromExprForRel(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                      bool use_alias, List **params_list)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

    if (IS_JOIN_REL(foreignrel))
    {
        StringInfoData join_sql_o;
        StringInfoData join_sql_i;

        /* Deparse outer relation */
        initStringInfo(&join_sql_o);
        deparseRangeTblRef(&join_sql_o, root, fpinfo->outerrel,
                           fpinfo->make_outerrel_subquery, params_list);

        /* Deparse inner relation */
        initStringInfo(&join_sql_i);
        deparseRangeTblRef(&join_sql_i, root, fpinfo->innerrel,
                           fpinfo->make_innerrel_subquery, params_list);

        /*
         * For a join relation FROM clause entry is deparsed as
         *
         * ((outer relation) <join type> (inner relation) ON (joinclauses))
         */
        appendStringInfo(buf, "(%s %s JOIN %s ON ", join_sql_o.data,
                         get_jointype_name(fpinfo->jointype), join_sql_i.data);

        /* Append join clause; (TRUE) if no join clause */
        if (fpinfo->joinclauses)
        {
            deparse_expr_cxt context;

            context.buf = buf;
            context.foreignrel = foreignrel;
            context.scanrel = foreignrel;
            context.root = root;
            context.params_list = params_list;

            appendStringInfo(buf, "(");
            appendConditions(fpinfo->joinclauses, &context);
            appendStringInfo(buf, ")");
        }
        else
            appendStringInfoString(buf, "(TRUE)");

        /* End the FROM clause entry. */
        appendStringInfo(buf, ")");
    }
    else
    {
        RangeTblEntry *rte = planner_rt_fetch(foreignrel->relid, root);

        /*
         * Core code already has some lock on each rel being planned, so we
         * can use NoLock here.
         */
        Relation    rel = heap_open(rte->relid, NoLock);

        deparseRelation(buf, rel);

        /*
         * Add a unique alias to avoid any conflict in relation names due to
         * pulled up subqueries in the query being built for a pushed down
         * join.
         */
        if (use_alias)
            appendStringInfo(buf, " %s%d", REL_ALIAS_PREFIX, foreignrel->relid);

        heap_close(rel, NoLock);
    }
}

/*
 * Append FROM clause entry for the given relation into buf.
 */
static void
deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
                   bool make_subquery, List **params_list)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;

    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

    Assert(fpinfo->local_conds == NIL);

    /* If make_subquery is true, deparse the relation as a subquery. */
    if (make_subquery)
    {
        List       *retrieved_attrs;
        int            ncols;

        /* Deparse the subquery representing the relation. */
        appendStringInfoChar(buf, '(');
        deparseSelectStmtForRel(buf, root, foreignrel, NIL,
                                fpinfo->remote_conds, NIL, true,
                                &retrieved_attrs, params_list);
        appendStringInfoChar(buf, ')');

        /* Append the relation alias. */
        appendStringInfo(buf, " %s%d", SUBQUERY_REL_ALIAS_PREFIX,
                         fpinfo->relation_index);

        /*
         * Append the column aliases if needed.  Note that the subquery emits
         * expressions specified in the relation's reltarget (see
         * deparseSubqueryTargetList).
         */
        ncols = list_length(foreignrel->reltarget->exprs);
        if (ncols > 0)
        {
            int            i;

            appendStringInfoChar(buf, '(');
            for (i = 1; i <= ncols; i++)
            {
                if (i > 1)
                    appendStringInfoString(buf, ", ");

                appendStringInfo(buf, "%s%d", SUBQUERY_COL_ALIAS_PREFIX, i);
            }
            appendStringInfoChar(buf, ')');
        }
    }
    else
        deparseFromExprForRel(buf, root, foreignrel, true, params_list);
}

/*
 * deparse remote INSERT statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseInsertSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *targetAttrs, bool doNothing,
                 List *returningList, List **retrieved_attrs)
{
    AttrNumber    pindex;
    bool        first;
    ListCell   *lc;

    appendStringInfoString(buf, "INSERT INTO ");
    deparseRelation(buf, rel);

    if (targetAttrs)
    {
        appendStringInfoChar(buf, '(');

        first = true;
        foreach(lc, targetAttrs)
        {
            int            attnum = lfirst_int(lc);

            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            deparseColumnRef(buf, rtindex, attnum, root, false);
        }

        appendStringInfoString(buf, ") VALUES (");

        pindex = 1;
        first = true;
        foreach(lc, targetAttrs)
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            appendStringInfo(buf, "$%d", pindex);
            pindex++;
        }

        appendStringInfoChar(buf, ')');
    }
    else
        appendStringInfoString(buf, " DEFAULT VALUES");

    if (doNothing)
        appendStringInfoString(buf, " ON CONFLICT DO NOTHING");

    deparseReturningList(buf, root, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_insert_after_row,
                         returningList, retrieved_attrs);
}

/*
 * deparse remote UPDATE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseUpdateSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *targetAttrs, List *returningList,
                 List **retrieved_attrs)
{
    AttrNumber    pindex;
    bool        first;
    ListCell   *lc;

    appendStringInfoString(buf, "UPDATE ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " SET ");

    pindex = 2;                    /* ctid is always the first param */
    first = true;
    foreach(lc, targetAttrs)
    {
        int            attnum = lfirst_int(lc);

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        deparseColumnRef(buf, rtindex, attnum, root, false);
        appendStringInfo(buf, " = $%d", pindex);
        pindex++;
    }
    appendStringInfoString(buf, " WHERE ctid = $1");

    deparseReturningList(buf, root, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_update_after_row,
                         returningList, retrieved_attrs);
}

/*
 * deparse remote UPDATE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDirectUpdateSql(StringInfo buf, PlannerInfo *root,
                       Index rtindex, Relation rel,
                       List *targetlist,
                       List *targetAttrs,
                       List *remote_conds,
                       List **params_list,
                       List *returningList,
                       List **retrieved_attrs)
{
    RelOptInfo *baserel = root->simple_rel_array[rtindex];
    deparse_expr_cxt context;
    int            nestlevel;
    bool        first;
    ListCell   *lc;

    /* Set up context struct for recursion */
    context.root = root;
    context.foreignrel = baserel;
    context.scanrel = baserel;
    context.buf = buf;
    context.params_list = params_list;

    appendStringInfoString(buf, "UPDATE ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " SET ");

    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();

    first = true;
    foreach(lc, targetAttrs)
    {
        int            attnum = lfirst_int(lc);
        TargetEntry *tle = get_tle_by_resno(targetlist, attnum);

        if (!tle)
            elog(ERROR, "attribute number %d not found in UPDATE targetlist",
                 attnum);

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        deparseColumnRef(buf, rtindex, attnum, root, false);
        appendStringInfoString(buf, " = ");
        deparseExpr((Expr *) tle->expr, &context);
    }

    reset_transmission_modes(nestlevel);

    if (remote_conds)
    {
        appendStringInfo(buf, " WHERE ");
        appendConditions(remote_conds, &context);
    }

    deparseReturningList(buf, root, rtindex, rel, false,
                         returningList, retrieved_attrs);
}

/*
 * deparse remote DELETE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDeleteSql(StringInfo buf, PlannerInfo *root,
                 Index rtindex, Relation rel,
                 List *returningList,
                 List **retrieved_attrs)
{
    appendStringInfoString(buf, "DELETE FROM ");
    deparseRelation(buf, rel);
    appendStringInfoString(buf, " WHERE ctid = $1");

    deparseReturningList(buf, root, rtindex, rel,
                         rel->trigdesc && rel->trigdesc->trig_delete_after_row,
                         returningList, retrieved_attrs);
}

/*
 * deparse remote DELETE statement
 *
 * The statement text is appended to buf, and we also create an integer List
 * of the columns being retrieved by RETURNING (if any), which is returned
 * to *retrieved_attrs.
 */
void
deparseDirectDeleteSql(StringInfo buf, PlannerInfo *root,
                       Index rtindex, Relation rel,
                       List *remote_conds,
                       List **params_list,
                       List *returningList,
                       List **retrieved_attrs)
{
    RelOptInfo *baserel = root->simple_rel_array[rtindex];
    deparse_expr_cxt context;

    /* Set up context struct for recursion */
    context.root = root;
    context.foreignrel = baserel;
    context.scanrel = baserel;
    context.buf = buf;
    context.params_list = params_list;

    appendStringInfoString(buf, "DELETE FROM ");
    deparseRelation(buf, rel);

    if (remote_conds)
    {
        appendStringInfo(buf, " WHERE ");
        appendConditions(remote_conds, &context);
    }

    deparseReturningList(buf, root, rtindex, rel, false,
                         returningList, retrieved_attrs);
}

/*
 * Add a RETURNING clause, if needed, to an INSERT/UPDATE/DELETE.
 */
static void
deparseReturningList(StringInfo buf, PlannerInfo *root,
                     Index rtindex, Relation rel,
                     bool trig_after_row,
                     List *returningList,
                     List **retrieved_attrs)
{
    Bitmapset  *attrs_used = NULL;

    if (trig_after_row)
    {
        /* whole-row reference acquires all non-system columns */
        attrs_used =
            bms_make_singleton(0 - FirstLowInvalidHeapAttributeNumber);
    }

    if (returningList != NIL)
    {
        /*
         * We need the attrs, non-system and system, mentioned in the local
         * query's RETURNING list.
         */
        pull_varattnos((Node *) returningList, rtindex,
                       &attrs_used);
    }

    if (attrs_used != NULL)
        deparseTargetList(buf, root, rtindex, rel, true, attrs_used, false,
                          retrieved_attrs);
    else
        *retrieved_attrs = NIL;
}

/*
 * Construct SELECT statement to acquire size in blocks of given relation.
 *
 * Note: we use local definition of block size, not remote definition.
 * This is perhaps debatable.
 *
 * Note: pg_relation_size() exists in 8.1 and later.
 */
void
deparseAnalyzeSizeSql(StringInfo buf, Relation rel)
{
    StringInfoData relname;

    /* We'll need the remote relation name as a literal. */
    initStringInfo(&relname);
    deparseRelation(&relname, rel);

    appendStringInfoString(buf, "SELECT pg_catalog.pg_relation_size(");
    deparseStringLiteral(buf, relname.data);
    appendStringInfo(buf, "::pg_catalog.regclass) / %d", BLCKSZ);
}

/*
 * Construct SELECT statement to acquire sample rows of given relation.
 *
 * SELECT command is appended to buf, and list of columns retrieved
 * is returned to *retrieved_attrs.
 */
void
deparseAnalyzeSql(StringInfo buf, Relation rel, List **retrieved_attrs)
{
    Oid            relid = RelationGetRelid(rel);
    TupleDesc    tupdesc = RelationGetDescr(rel);
    int            i;
    char       *colname;
    List       *options;
    ListCell   *lc;
    bool        first = true;

    *retrieved_attrs = NIL;

    appendStringInfoString(buf, "SELECT ");
    for (i = 0; i < tupdesc->natts; i++)
    {
        /* Ignore dropped columns. */
        if (tupdesc->attrs[i]->attisdropped)
            continue;

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        /* Use attribute name or column_name option. */
        colname = NameStr(tupdesc->attrs[i]->attname);
        options = GetForeignColumnOptions(relid, i + 1);

        foreach(lc, options)
        {
            DefElem    *def = (DefElem *) lfirst(lc);

            if (strcmp(def->defname, "column_name") == 0)
            {
                colname = defGetString(def);
                break;
            }
        }

        appendStringInfoString(buf, quote_identifier(colname));

        *retrieved_attrs = lappend_int(*retrieved_attrs, i + 1);
    }

    /* Don't generate bad syntax for zero-column relation. */
    if (first)
        appendStringInfoString(buf, "NULL");

    /*
     * Construct FROM clause
     */
    appendStringInfoString(buf, " FROM ");
    deparseRelation(buf, rel);
}

/*
 * Construct name to use for given column, and emit it into buf.
 * If it has a column_name FDW option, use that instead of attribute name.
 *
 * If qualify_col is true, qualify column name with the alias of relation.
 */
static void
deparseColumnRef(StringInfo buf, int varno, int varattno, PlannerInfo *root,
                 bool qualify_col)
{
    RangeTblEntry *rte;

    /* We support fetching the remote side's CTID and OID. */
    if (varattno == SelfItemPointerAttributeNumber)
    {
        if (qualify_col)
            ADD_REL_QUALIFIER(buf, varno);
        appendStringInfoString(buf, "ctid");
    }
    else if (varattno == ObjectIdAttributeNumber)
    {
        if (qualify_col)
            ADD_REL_QUALIFIER(buf, varno);
        appendStringInfoString(buf, "oid");
    }
    else if (varattno < 0)
    {
        /*
         * All other system attributes are fetched as 0, except for table OID,
         * which is fetched as the local table OID.  However, we must be
         * careful; the table could be beneath an outer join, in which case it
         * must go to NULL whenever the rest of the row does.
         */
        Oid            fetchval = 0;

        if (varattno == TableOidAttributeNumber)
        {
            rte = planner_rt_fetch(varno, root);
            fetchval = rte->relid;
        }

        if (qualify_col)
        {
            appendStringInfoString(buf, "CASE WHEN (");
            ADD_REL_QUALIFIER(buf, varno);
            appendStringInfo(buf, "*)::text IS NOT NULL THEN %u END", fetchval);
        }
        else
            appendStringInfo(buf, "%u", fetchval);
    }
    else if (varattno == 0)
    {
        /* Whole row reference */
        Relation    rel;
        Bitmapset  *attrs_used;

        /* Required only to be passed down to deparseTargetList(). */
        List       *retrieved_attrs;

        /* Get RangeTblEntry from array in PlannerInfo. */
        rte = planner_rt_fetch(varno, root);

        /*
         * The lock on the relation will be held by upper callers, so it's
         * fine to open it with no lock here.
         */
        rel = heap_open(rte->relid, NoLock);

        /*
         * The local name of the foreign table can not be recognized by the
         * foreign server and the table it references on foreign server might
         * have different column ordering or different columns than those
         * declared locally. Hence we have to deparse whole-row reference as
         * ROW(columns referenced locally). Construct this by deparsing a
         * "whole row" attribute.
         */
        attrs_used = bms_add_member(NULL,
                                    0 - FirstLowInvalidHeapAttributeNumber);

        /*
         * In case the whole-row reference is under an outer join then it has
         * to go NULL whenever the rest of the row goes NULL. Deparsing a join
         * query would always involve multiple relations, thus qualify_col
         * would be true.
         */
        if (qualify_col)
        {
            appendStringInfoString(buf, "CASE WHEN (");
            ADD_REL_QUALIFIER(buf, varno);
            appendStringInfo(buf, "*)::text IS NOT NULL THEN ");
        }

        appendStringInfoString(buf, "ROW(");
        deparseTargetList(buf, root, varno, rel, false, attrs_used, qualify_col,
                          &retrieved_attrs);
        appendStringInfoString(buf, ")");

        /* Complete the CASE WHEN statement started above. */
        if (qualify_col)
            appendStringInfo(buf, " END");

        heap_close(rel, NoLock);
        bms_free(attrs_used);
    }
    else
    {
        char       *colname = NULL;
        List       *options;
        ListCell   *lc;

        /* varno must not be any of OUTER_VAR, INNER_VAR and INDEX_VAR. */
        Assert(!IS_SPECIAL_VARNO(varno));

        /* Get RangeTblEntry from array in PlannerInfo. */
        rte = planner_rt_fetch(varno, root);

        /*
         * If it's a column of a foreign table, and it has the column_name FDW
         * option, use that value.
         */
        options = GetForeignColumnOptions(rte->relid, varattno);
        foreach(lc, options)
        {
            DefElem    *def = (DefElem *) lfirst(lc);

            if (strcmp(def->defname, "column_name") == 0)
            {
                colname = defGetString(def);
                break;
            }
        }

        /*
         * If it's a column of a regular table or it doesn't have column_name
         * FDW option, use attribute name.
         */
        if (colname == NULL)
            colname = get_relid_attribute_name(rte->relid, varattno);

        if (qualify_col)
            ADD_REL_QUALIFIER(buf, varno);

        appendStringInfoString(buf, quote_identifier(colname));
    }
}

/*
 * Append remote name of specified foreign table to buf.
 * Use value of table_name FDW option (if any) instead of relation's name.
 * Similarly, schema_name FDW option overrides schema name.
 */
static void
deparseRelation(StringInfo buf, Relation rel)
{
    ForeignTable *table;
    const char *nspname = NULL;
    const char *relname = NULL;
    ListCell   *lc;

    /* obtain additional catalog information. */
    table = GetForeignTable(RelationGetRelid(rel));

    /*
     * Use value of FDW options if any, instead of the name of object itself.
     */
    foreach(lc, table->options)
    {
        DefElem    *def = (DefElem *) lfirst(lc);

        if (strcmp(def->defname, "schema_name") == 0)
            nspname = defGetString(def);
        else if (strcmp(def->defname, "table_name") == 0)
            relname = defGetString(def);
    }

    /*
     * Note: we could skip printing the schema name if it's pg_catalog, but
     * that doesn't seem worth the trouble.
     */
    if (nspname == NULL)
        nspname = get_namespace_name(RelationGetNamespace(rel));
    if (relname == NULL)
        relname = RelationGetRelationName(rel);

    appendStringInfo(buf, "%s.%s",
                     quote_identifier(nspname), quote_identifier(relname));
}

/*
 * Append a SQL string literal representing "val" to buf.
 */
void
deparseStringLiteral(StringInfo buf, const char *val)
{
    const char *valptr;

    /*
     * Rather than making assumptions about the remote server's value of
     * standard_conforming_strings, always use E'foo' syntax if there are any
     * backslashes.  This will fail on remote servers before 8.1, but those
     * are long out of support.
     */
    if (strchr(val, '\\') != NULL)
        appendStringInfoChar(buf, ESCAPE_STRING_SYNTAX);
    appendStringInfoChar(buf, '\'');
    for (valptr = val; *valptr; valptr++)
    {
        char        ch = *valptr;

        if (SQL_STR_DOUBLE(ch, true))
            appendStringInfoChar(buf, ch);
        appendStringInfoChar(buf, ch);
    }
    appendStringInfoChar(buf, '\'');
}

/*
 * Deparse given expression into context->buf.
 *
 * This function must support all the same node types that foreign_expr_walker
 * accepts.
 *
 * Note: unlike ruleutils.c, we just use a simple hard-wired parenthesization
 * scheme: anything more complex than a Var, Const, function call or cast
 * should be self-parenthesized.
 */
static void
deparseExpr(Expr *node, deparse_expr_cxt *context)
{
    if (node == NULL)
        return;

    switch (nodeTag(node))
    {
        case T_Var:
            deparseVar((Var *) node, context);
            break;
        case T_Const:
            deparseConst((Const *) node, context, 0);
            break;
        case T_Param:
            deparseParam((Param *) node, context);
            break;
        case T_ArrayRef:
            deparseArrayRef((ArrayRef *) node, context);
            break;
        case T_FuncExpr:
            deparseFuncExpr((FuncExpr *) node, context);
            break;
        case T_OpExpr:
            deparseOpExpr((OpExpr *) node, context);
            break;
        case T_DistinctExpr:
            deparseDistinctExpr((DistinctExpr *) node, context);
            break;
        case T_ScalarArrayOpExpr:
            deparseScalarArrayOpExpr((ScalarArrayOpExpr *) node, context);
            break;
        case T_RelabelType:
            deparseRelabelType((RelabelType *) node, context);
            break;
        case T_BoolExpr:
            deparseBoolExpr((BoolExpr *) node, context);
            break;
        case T_NullTest:
            deparseNullTest((NullTest *) node, context);
            break;
        case T_ArrayExpr:
            deparseArrayExpr((ArrayExpr *) node, context);
            break;
        case T_Aggref:
            deparseAggref((Aggref *) node, context);
            break;
        default:
            elog(ERROR, "unsupported expression type for deparse: %d",
                 (int) nodeTag(node));
            break;
    }
}

/*
 * Deparse given Var node into context->buf.
 *
 * If the Var belongs to the foreign relation, just print its remote name.
 * Otherwise, it's effectively a Param (and will in fact be a Param at
 * run time).  Handle it the same way we handle plain Params --- see
 * deparseParam for comments.
 */
static void
deparseVar(Var *node, deparse_expr_cxt *context)
{
    Relids        relids = context->scanrel->relids;
    int            relno;
    int            colno;

    /* Qualify columns when multiple relations are involved. */
    bool        qualify_col = (bms_num_members(relids) > 1);

    /*
     * If the Var belongs to the foreign relation that is deparsed as a
     * subquery, use the relation and column alias to the Var provided by the
     * subquery, instead of the remote name.
     */
    if (is_subquery_var(node, context->scanrel, &relno, &colno))
    {
        appendStringInfo(context->buf, "%s%d.%s%d",
                         SUBQUERY_REL_ALIAS_PREFIX, relno,
                         SUBQUERY_COL_ALIAS_PREFIX, colno);
        return;
    }

    if (bms_is_member(node->varno, relids) && node->varlevelsup == 0)
        deparseColumnRef(context->buf, node->varno, node->varattno,
                         context->root, qualify_col);
    else
    {
        /* Treat like a Param */
        if (context->params_list)
        {
            int            pindex = 0;
            ListCell   *lc;

            /* find its index in params_list */
            foreach(lc, *context->params_list)
            {
                pindex++;
                if (equal(node, (Node *) lfirst(lc)))
                    break;
            }
            if (lc == NULL)
            {
                /* not in list, so add it */
                pindex++;
                *context->params_list = lappend(*context->params_list, node);
            }

            printRemoteParam(pindex, node->vartype, node->vartypmod, context);
        }
        else
        {
            printRemotePlaceholder(node->vartype, node->vartypmod, context);
        }
    }
}

/*
 * Deparse given constant value into context->buf.
 *
 * This function has to be kept in sync with ruleutils.c's get_const_expr.
 * As for that function, showtype can be -1 to never show "::typename" decoration,
 * or +1 to always show it, or 0 to show it only if the constant wouldn't be assumed
 * to be the right type by default.
 */
static void
deparseConst(Const *node, deparse_expr_cxt *context, int showtype)
{
    StringInfo    buf = context->buf;
    Oid            typoutput;
    bool        typIsVarlena;
    char       *extval;
    bool        isfloat = false;
    bool        needlabel;

    if (node->constisnull)
    {
        appendStringInfoString(buf, "NULL");
        if (showtype >= 0)
            appendStringInfo(buf, "::%s",
                             deparse_type_name(node->consttype,
                                               node->consttypmod));
        return;
    }

    getTypeOutputInfo(node->consttype,
                      &typoutput, &typIsVarlena);
    extval = OidOutputFunctionCall(typoutput, node->constvalue);

    switch (node->consttype)
    {
        case INT2OID:
        case INT4OID:
        case INT8OID:
        case OIDOID:
        case FLOAT4OID:
        case FLOAT8OID:
        case NUMERICOID:
            {
                /*
                 * No need to quote unless it's a special value such as 'NaN'.
                 * See comments in get_const_expr().
                 */
                if (strspn(extval, "0123456789+-eE.") == strlen(extval))
                {
                    if (extval[0] == '+' || extval[0] == '-')
                        appendStringInfo(buf, "(%s)", extval);
                    else
                        appendStringInfoString(buf, extval);
                    if (strcspn(extval, "eE.") != strlen(extval))
                        isfloat = true; /* it looks like a float */
                }
                else
                    appendStringInfo(buf, "'%s'", extval);
            }
            break;
        case BITOID:
        case VARBITOID:
            appendStringInfo(buf, "B'%s'", extval);
            break;
        case BOOLOID:
            if (strcmp(extval, "t") == 0)
                appendStringInfoString(buf, "true");
            else
                appendStringInfoString(buf, "false");
            break;
        default:
            deparseStringLiteral(buf, extval);
            break;
    }

    pfree(extval);

    if (showtype < 0)
        return;

    /*
     * For showtype == 0, append ::typename unless the constant will be
     * implicitly typed as the right type when it is read in.
     *
     * XXX this code has to be kept in sync with the behavior of the parser,
     * especially make_const.
     */
    switch (node->consttype)
    {
        case BOOLOID:
        case INT4OID:
        case UNKNOWNOID:
            needlabel = false;
            break;
        case NUMERICOID:
            needlabel = !isfloat || (node->consttypmod >= 0);
            break;
        default:
            needlabel = true;
            break;
    }
    if (needlabel || showtype > 0)
        appendStringInfo(buf, "::%s",
                         deparse_type_name(node->consttype,
                                           node->consttypmod));
}

/*
 * Deparse given Param node.
 *
 * If we're generating the query "for real", add the Param to
 * context->params_list if it's not already present, and then use its index
 * in that list as the remote parameter number.  During EXPLAIN, there's
 * no need to identify a parameter number.
 */
static void
deparseParam(Param *node, deparse_expr_cxt *context)
{
    if (context->params_list)
    {
        int            pindex = 0;
        ListCell   *lc;

        /* find its index in params_list */
        foreach(lc, *context->params_list)
        {
            pindex++;
            if (equal(node, (Node *) lfirst(lc)))
                break;
        }
        if (lc == NULL)
        {
            /* not in list, so add it */
            pindex++;
            *context->params_list = lappend(*context->params_list, node);
        }

        printRemoteParam(pindex, node->paramtype, node->paramtypmod, context);
    }
    else
    {
        printRemotePlaceholder(node->paramtype, node->paramtypmod, context);
    }
}

/*
 * Deparse an array subscript expression.
 */
static void
deparseArrayRef(ArrayRef *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    ListCell   *lowlist_item;
    ListCell   *uplist_item;

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /*
     * Deparse referenced array expression first.  If that expression includes
     * a cast, we have to parenthesize to prevent the array subscript from
     * being taken as typename decoration.  We can avoid that in the typical
     * case of subscripting a Var, but otherwise do it.
     */
    if (IsA(node->refexpr, Var))
        deparseExpr(node->refexpr, context);
    else
    {
        appendStringInfoChar(buf, '(');
        deparseExpr(node->refexpr, context);
        appendStringInfoChar(buf, ')');
    }

    /* Deparse subscript expressions. */
    lowlist_item = list_head(node->reflowerindexpr);    /* could be NULL */
    foreach(uplist_item, node->refupperindexpr)
    {
        appendStringInfoChar(buf, '[');
        if (lowlist_item)
        {
            deparseExpr(lfirst(lowlist_item), context);
            appendStringInfoChar(buf, ':');
            lowlist_item = lnext(lowlist_item);
        }
        deparseExpr(lfirst(uplist_item), context);
        appendStringInfoChar(buf, ']');
    }

    appendStringInfoChar(buf, ')');
}

/*
 * Deparse a function call.
 */
static void
deparseFuncExpr(FuncExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    bool        use_variadic;
    bool        first;
    ListCell   *arg;

    /*
     * If the function call came from an implicit coercion, then just show the
     * first argument.
     */
    if (node->funcformat == COERCE_IMPLICIT_CAST)
    {
        deparseExpr((Expr *) linitial(node->args), context);
        return;
    }

    /*
     * If the function call came from a cast, then show the first argument
     * plus an explicit cast operation.
     */
    if (node->funcformat == COERCE_EXPLICIT_CAST)
    {
        Oid            rettype = node->funcresulttype;
        int32        coercedTypmod;

        /* Get the typmod if this is a length-coercion function */
        (void) exprIsLengthCoercion((Node *) node, &coercedTypmod);

        deparseExpr((Expr *) linitial(node->args), context);
        appendStringInfo(buf, "::%s",
                         deparse_type_name(rettype, coercedTypmod));
        return;
    }

    /* Check if need to print VARIADIC (cf. ruleutils.c) */
    use_variadic = node->funcvariadic;

    /*
     * Normal function: display as proname(args).
     */
    appendFunctionName(node->funcid, context);
    appendStringInfoChar(buf, '(');

    /* ... and all the arguments */
    first = true;
    foreach(arg, node->args)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        if (use_variadic && lnext(arg) == NULL)
            appendStringInfoString(buf, "VARIADIC ");
        deparseExpr((Expr *) lfirst(arg), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');
}

/*
 * Deparse given operator expression.   To avoid problems around
 * priority of operations, we always parenthesize the arguments.
 */
static void
deparseOpExpr(OpExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    HeapTuple    tuple;
    Form_pg_operator form;
    char        oprkind;
    ListCell   *arg;

    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);
    oprkind = form->oprkind;

    /* Sanity check. */
    Assert((oprkind == 'r' && list_length(node->args) == 1) ||
           (oprkind == 'l' && list_length(node->args) == 1) ||
           (oprkind == 'b' && list_length(node->args) == 2));

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /* Deparse left operand. */
    if (oprkind == 'r' || oprkind == 'b')
    {
        arg = list_head(node->args);
        deparseExpr(lfirst(arg), context);
        appendStringInfoChar(buf, ' ');
    }

    /* Deparse operator name. */
    deparseOperatorName(buf, form);

    /* Deparse right operand. */
    if (oprkind == 'l' || oprkind == 'b')
    {
        arg = list_tail(node->args);
        appendStringInfoChar(buf, ' ');
        deparseExpr(lfirst(arg), context);
    }

    appendStringInfoChar(buf, ')');

    ReleaseSysCache(tuple);
}

/*
 * Print the name of an operator.
 */
static void
deparseOperatorName(StringInfo buf, Form_pg_operator opform)
{
    char       *opname;

    /* opname is not a SQL identifier, so we should not quote it. */
    opname = NameStr(opform->oprname);

    /* Print schema name only if it's not pg_catalog */
    if (opform->oprnamespace != PG_CATALOG_NAMESPACE)
    {
        const char *opnspname;

        opnspname = get_namespace_name(opform->oprnamespace);
        /* Print fully qualified operator name. */
        appendStringInfo(buf, "OPERATOR(%s.%s)",
                         quote_identifier(opnspname), opname);
    }
    else
    {
        /* Just print operator name. */
        appendStringInfoString(buf, opname);
    }
}

/*
 * Deparse IS DISTINCT FROM.
 */
static void
deparseDistinctExpr(DistinctExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;

    Assert(list_length(node->args) == 2);

    appendStringInfoChar(buf, '(');
    deparseExpr(linitial(node->args), context);
    appendStringInfoString(buf, " IS DISTINCT FROM ");
    deparseExpr(lsecond(node->args), context);
    appendStringInfoChar(buf, ')');
}

/*
 * Deparse given ScalarArrayOpExpr expression.  To avoid problems
 * around priority of operations, we always parenthesize the arguments.
 */
static void
deparseScalarArrayOpExpr(ScalarArrayOpExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    HeapTuple    tuple;
    Form_pg_operator form;
    Expr       *arg1;
    Expr       *arg2;

    /* Retrieve information about the operator from system catalog. */
    tuple = SearchSysCache1(OPEROID, ObjectIdGetDatum(node->opno));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for operator %u", node->opno);
    form = (Form_pg_operator) GETSTRUCT(tuple);

    /* Sanity check. */
    Assert(list_length(node->args) == 2);

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, '(');

    /* Deparse left operand. */
    arg1 = linitial(node->args);
    deparseExpr(arg1, context);
    appendStringInfoChar(buf, ' ');

    /* Deparse operator name plus decoration. */
    deparseOperatorName(buf, form);
    appendStringInfo(buf, " %s (", node->useOr ? "ANY" : "ALL");

    /* Deparse right operand. */
    arg2 = lsecond(node->args);
    deparseExpr(arg2, context);

    appendStringInfoChar(buf, ')');

    /* Always parenthesize the expression. */
    appendStringInfoChar(buf, ')');

    ReleaseSysCache(tuple);
}

/*
 * Deparse a RelabelType (binary-compatible cast) node.
 */
static void
deparseRelabelType(RelabelType *node, deparse_expr_cxt *context)
{
    deparseExpr(node->arg, context);
    if (node->relabelformat != COERCE_IMPLICIT_CAST)
        appendStringInfo(context->buf, "::%s",
                         deparse_type_name(node->resulttype,
                                           node->resulttypmod));
}

/*
 * Deparse a BoolExpr node.
 */
static void
deparseBoolExpr(BoolExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    const char *op = NULL;        /* keep compiler quiet */
    bool        first;
    ListCell   *lc;

    switch (node->boolop)
    {
        case AND_EXPR:
            op = "AND";
            break;
        case OR_EXPR:
            op = "OR";
            break;
        case NOT_EXPR:
            appendStringInfoString(buf, "(NOT ");
            deparseExpr(linitial(node->args), context);
            appendStringInfoChar(buf, ')');
            return;
    }

    appendStringInfoChar(buf, '(');
    first = true;
    foreach(lc, node->args)
    {
        if (!first)
            appendStringInfo(buf, " %s ", op);
        deparseExpr((Expr *) lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ')');
}

/*
 * Deparse IS [NOT] NULL expression.
 */
static void
deparseNullTest(NullTest *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;

    appendStringInfoChar(buf, '(');
    deparseExpr(node->arg, context);

    /*
     * For scalar inputs, we prefer to print as IS [NOT] NULL, which is
     * shorter and traditional.  If it's a rowtype input but we're applying a
     * scalar test, must print IS [NOT] DISTINCT FROM NULL to be semantically
     * correct.
     */
    if (node->argisrow || !type_is_rowtype(exprType((Node *) node->arg)))
    {
        if (node->nulltesttype == IS_NULL)
            appendStringInfoString(buf, " IS NULL)");
        else
            appendStringInfoString(buf, " IS NOT NULL)");
    }
    else
    {
        if (node->nulltesttype == IS_NULL)
            appendStringInfoString(buf, " IS NOT DISTINCT FROM NULL)");
        else
            appendStringInfoString(buf, " IS DISTINCT FROM NULL)");
    }
}

/*
 * Deparse ARRAY[...] construct.
 */
static void
deparseArrayExpr(ArrayExpr *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    bool        first = true;
    ListCell   *lc;

    appendStringInfoString(buf, "ARRAY[");
    foreach(lc, node->elements)
    {
        if (!first)
            appendStringInfoString(buf, ", ");
        deparseExpr(lfirst(lc), context);
        first = false;
    }
    appendStringInfoChar(buf, ']');

    /* If the array is empty, we need an explicit cast to the array type. */
    if (node->elements == NIL)
        appendStringInfo(buf, "::%s",
                         deparse_type_name(node->array_typeid, -1));
}

/*
 * Deparse an Aggref node.
 */
static void
deparseAggref(Aggref *node, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    bool        use_variadic;

    /* Only basic, non-split aggregation accepted. */
    Assert(node->aggsplit == AGGSPLIT_SIMPLE);

    /* Check if need to print VARIADIC (cf. ruleutils.c) */
    use_variadic = node->aggvariadic;

    /* Find aggregate name from aggfnoid which is a pg_proc entry */
    appendFunctionName(node->aggfnoid, context);
    appendStringInfoChar(buf, '(');

    /* Add DISTINCT */
    appendStringInfo(buf, "%s", (node->aggdistinct != NIL) ? "DISTINCT " : "");

    if (AGGKIND_IS_ORDERED_SET(node->aggkind))
    {
        /* Add WITHIN GROUP (ORDER BY ..) */
        ListCell   *arg;
        bool        first = true;

        Assert(!node->aggvariadic);
        Assert(node->aggorder != NIL);

        foreach(arg, node->aggdirectargs)
        {
            if (!first)
                appendStringInfoString(buf, ", ");
            first = false;

            deparseExpr((Expr *) lfirst(arg), context);
        }

        appendStringInfoString(buf, ") WITHIN GROUP (ORDER BY ");
        appendAggOrderBy(node->aggorder, node->args, context);
    }
    else
    {
        /* aggstar can be set only in zero-argument aggregates */
        if (node->aggstar)
            appendStringInfoChar(buf, '*');
        else
        {
            ListCell   *arg;
            bool        first = true;

            /* Add all the arguments */
            foreach(arg, node->args)
            {
                TargetEntry *tle = (TargetEntry *) lfirst(arg);
                Node       *n = (Node *) tle->expr;

                if (tle->resjunk)
                    continue;

                if (!first)
                    appendStringInfoString(buf, ", ");
                first = false;

                /* Add VARIADIC */
                if (use_variadic && lnext(arg) == NULL)
                    appendStringInfoString(buf, "VARIADIC ");

                deparseExpr((Expr *) n, context);
            }
        }

        /* Add ORDER BY */
        if (node->aggorder != NIL)
        {
            appendStringInfoString(buf, " ORDER BY ");
            appendAggOrderBy(node->aggorder, node->args, context);
        }
    }

    /* Add FILTER (WHERE ..) */
    if (node->aggfilter != NULL)
    {
        appendStringInfoString(buf, ") FILTER (WHERE ");
        deparseExpr((Expr *) node->aggfilter, context);
    }

    appendStringInfoChar(buf, ')');
}

/*
 * Append ORDER BY within aggregate function.
 */
static void
appendAggOrderBy(List *orderList, List *targetList, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    ListCell   *lc;
    bool        first = true;

    foreach(lc, orderList)
    {
        SortGroupClause *srt = (SortGroupClause *) lfirst(lc);
        Node       *sortexpr;
        Oid            sortcoltype;
        TypeCacheEntry *typentry;

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        sortexpr = deparseSortGroupClause(srt->tleSortGroupRef, targetList,
                                          context);
        sortcoltype = exprType(sortexpr);
        /* See whether operator is default < or > for datatype */
        typentry = lookup_type_cache(sortcoltype,
                                     TYPECACHE_LT_OPR | TYPECACHE_GT_OPR);
        if (srt->sortop == typentry->lt_opr)
            appendStringInfoString(buf, " ASC");
        else if (srt->sortop == typentry->gt_opr)
            appendStringInfoString(buf, " DESC");
        else
        {
            HeapTuple    opertup;
            Form_pg_operator operform;

            appendStringInfoString(buf, " USING ");

            /* Append operator name. */
            opertup = SearchSysCache1(OPEROID, ObjectIdGetDatum(srt->sortop));
            if (!HeapTupleIsValid(opertup))
                elog(ERROR, "cache lookup failed for operator %u", srt->sortop);
            operform = (Form_pg_operator) GETSTRUCT(opertup);
            deparseOperatorName(buf, operform);
            ReleaseSysCache(opertup);
        }

        if (srt->nulls_first)
            appendStringInfoString(buf, " NULLS FIRST");
        else
            appendStringInfoString(buf, " NULLS LAST");
    }
}

/*
 * Print the representation of a parameter to be sent to the remote side.
 *
 * Note: we always label the Param's type explicitly rather than relying on
 * transmitting a numeric type OID in PQexecParams().  This allows us to
 * avoid assuming that types have the same OIDs on the remote side as they
 * do locally --- they need only have the same names.
 */
static void
printRemoteParam(int paramindex, Oid paramtype, int32 paramtypmod,
                 deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    char       *ptypename = deparse_type_name(paramtype, paramtypmod);

    appendStringInfo(buf, "$%d::%s", paramindex, ptypename);
}

/*
 * Print the representation of a placeholder for a parameter that will be
 * sent to the remote side at execution time.
 *
 * This is used when we're just trying to EXPLAIN the remote query.
 * We don't have the actual value of the runtime parameter yet, and we don't
 * want the remote planner to generate a plan that depends on such a value
 * anyway.  Thus, we can't do something simple like "$1::paramtype".
 * Instead, we emit "((SELECT null::paramtype)::paramtype)".
 * In all extant versions of Postgres, the planner will see that as an unknown
 * constant value, which is what we want.  This might need adjustment if we
 * ever make the planner flatten scalar subqueries.  Note: the reason for the
 * apparently useless outer cast is to ensure that the representation as a
 * whole will be parsed as an a_expr and not a select_with_parens; the latter
 * would do the wrong thing in the context "x = ANY(...)".
 */
static void
printRemotePlaceholder(Oid paramtype, int32 paramtypmod,
                       deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    char       *ptypename = deparse_type_name(paramtype, paramtypmod);

    appendStringInfo(buf, "((SELECT null::%s)::%s)", ptypename, ptypename);
}

/*
 * Deparse GROUP BY clause.
 */
static void
appendGroupByClause(List *tlist, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    Query       *query = context->root->parse;
    ListCell   *lc;
    bool        first = true;

    /* Nothing to be done, if there's no GROUP BY clause in the query. */
    if (!query->groupClause)
        return;

    appendStringInfo(buf, " GROUP BY ");

    /*
     * Queries with grouping sets are not pushed down, so we don't expect
     * grouping sets here.
     */
    Assert(!query->groupingSets);

    foreach(lc, query->groupClause)
    {
        SortGroupClause *grp = (SortGroupClause *) lfirst(lc);

        if (!first)
            appendStringInfoString(buf, ", ");
        first = false;

        deparseSortGroupClause(grp->tleSortGroupRef, tlist, context);
    }
}

/*
 * Deparse ORDER BY clause according to the given pathkeys for given base
 * relation. From given pathkeys expressions belonging entirely to the given
 * base relation are obtained and deparsed.
 */
static void
appendOrderByClause(List *pathkeys, deparse_expr_cxt *context)
{
    ListCell   *lcell;
    int            nestlevel;
    char       *delim = " ";
    RelOptInfo *baserel = context->scanrel;
    StringInfo    buf = context->buf;

    /* Make sure any constants in the exprs are printed portably */
    nestlevel = set_transmission_modes();

    appendStringInfo(buf, " ORDER BY");
    foreach(lcell, pathkeys)
    {
        PathKey    *pathkey = lfirst(lcell);
        Expr       *em_expr;

        em_expr = find_em_expr_for_rel(pathkey->pk_eclass, baserel);
        Assert(em_expr != NULL);

        appendStringInfoString(buf, delim);
        deparseExpr(em_expr, context);
        if (pathkey->pk_strategy == BTLessStrategyNumber)
            appendStringInfoString(buf, " ASC");
        else
            appendStringInfoString(buf, " DESC");

        if (pathkey->pk_nulls_first)
            appendStringInfoString(buf, " NULLS FIRST");
        else
            appendStringInfoString(buf, " NULLS LAST");

        delim = ", ";
    }
    reset_transmission_modes(nestlevel);
}

/*
 * appendFunctionName
 *        Deparses function name from given function oid.
 */
static void
appendFunctionName(Oid funcid, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    HeapTuple    proctup;
    Form_pg_proc procform;
    const char *proname;

    proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(funcid));
    if (!HeapTupleIsValid(proctup))
        elog(ERROR, "cache lookup failed for function %u", funcid);
    procform = (Form_pg_proc) GETSTRUCT(proctup);

    /* Print schema name only if it's not pg_catalog */
    if (procform->pronamespace != PG_CATALOG_NAMESPACE)
    {
        const char *schemaname;

        schemaname = get_namespace_name(procform->pronamespace);
        appendStringInfo(buf, "%s.", quote_identifier(schemaname));
    }

    /* Always print the function name */
    proname = NameStr(procform->proname);
    appendStringInfo(buf, "%s", quote_identifier(proname));

    ReleaseSysCache(proctup);
}

/*
 * Appends a sort or group clause.
 *
 * Like get_rule_sortgroupclause(), returns the expression tree, so caller
 * need not find it again.
 */
static Node *
deparseSortGroupClause(Index ref, List *tlist, deparse_expr_cxt *context)
{
    StringInfo    buf = context->buf;
    TargetEntry *tle;
    Expr       *expr;

    tle = get_sortgroupref_tle(ref, tlist);
    expr = tle->expr;

    if (expr && IsA(expr, Const))
    {
        /*
         * Force a typecast here so that we don't emit something like "GROUP
         * BY 2", which will be misconstrued as a column position rather than
         * a constant.
         */
        deparseConst((Const *) expr, context, 1);
    }
    else if (!expr || IsA(expr, Var))
        deparseExpr(expr, context);
    else
    {
        /* Always parenthesize the expression. */
        appendStringInfoString(buf, "(");
        deparseExpr(expr, context);
        appendStringInfoString(buf, ")");
    }

    return (Node *) expr;
}


/*
 * Returns true if given Var is deparsed as a subquery output column, in
 * which case, *relno and *colno are set to the IDs for the relation and
 * column alias to the Var provided by the subquery.
 */
static bool
is_subquery_var(Var *node, RelOptInfo *foreignrel, int *relno, int *colno)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    RelOptInfo *outerrel = fpinfo->outerrel;
    RelOptInfo *innerrel = fpinfo->innerrel;

    /* Should only be called in these cases. */
    Assert(IS_SIMPLE_REL(foreignrel) || IS_JOIN_REL(foreignrel));

    /*
     * If the given relation isn't a join relation, it doesn't have any lower
     * subqueries, so the Var isn't a subquery output column.
     */
    if (!IS_JOIN_REL(foreignrel))
        return false;

    /*
     * If the Var doesn't belong to any lower subqueries, it isn't a subquery
     * output column.
     */
    if (!bms_is_member(node->varno, fpinfo->lower_subquery_rels))
        return false;

    if (bms_is_member(node->varno, outerrel->relids))
    {
        /*
         * If outer relation is deparsed as a subquery, the Var is an output
         * column of the subquery; get the IDs for the relation/column alias.
         */
        if (fpinfo->make_outerrel_subquery)
        {
            get_relation_column_alias_ids(node, outerrel, relno, colno);
            return true;
        }

        /* Otherwise, recurse into the outer relation. */
        return is_subquery_var(node, outerrel, relno, colno);
    }
    else
    {
        Assert(bms_is_member(node->varno, innerrel->relids));

        /*
         * If inner relation is deparsed as a subquery, the Var is an output
         * column of the subquery; get the IDs for the relation/column alias.
         */
        if (fpinfo->make_innerrel_subquery)
        {
            get_relation_column_alias_ids(node, innerrel, relno, colno);
            return true;
        }

        /* Otherwise, recurse into the inner relation. */
        return is_subquery_var(node, innerrel, relno, colno);
    }
}

/*
 * Get the IDs for the relation and column alias to given Var belonging to
 * given relation, which are returned into *relno and *colno.
 */
static void
get_relation_column_alias_ids(Var *node, RelOptInfo *foreignrel,
                              int *relno, int *colno)
{
    PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) foreignrel->fdw_private;
    int            i;
    ListCell   *lc;

    /* Get the relation alias ID */
    *relno = fpinfo->relation_index;

    /* Get the column alias ID */
    i = 1;
    foreach(lc, foreignrel->reltarget->exprs)
    {
        if (equal(lfirst(lc), (Node *) node))
        {
            *colno = i;
            return;
        }
        i++;
    }

    /* Shouldn't get here */
    elog(ERROR, "unexpected expression in subquery output");
}
